The present invention relates to an optical type information recording medium for optically recording information in response to radiation of a laser beam, and, more particularly, to an optical type information recording medium for recording information by forming local projections on a recording layer upon radiation of a write laser beam, and a manufacturing method therefor.
A conventional optical disk is known as an optical type recording medium having a recording layer which is locally projected in response to a laser beam. A typical recording layer of the optical disk of this type comprises a metal layer for absorbing laser beam energy, and an interlayer which is made of an organic material and which emits a gas component in response to beam energy. In general, the energy absorbing metal layer is locally heated to indirectly heat and decompose the organic interlayer which then generates a gas contained therein. A surface of the metal layer then acquires local projections as a result of the pressure of the gas produced from the organic interlayer. When a pulsated write laser beam, representing digital information, irradiates the optical disk, continuous concentric or spiral protuberances are formed on the surface of the metal layer in accordance with the mechanism described above, thereby storing the digital information.
According to the conventional optical disk of this type, the organic interlayer is indirectly heated and the utilization efficiency of the laser beam is greatly degraded. A high power laser beam must be used to form projectios, resulting in inconvenience. Since the recording layer comprises a multilayer structure, the manufacturing process is so complicated as to decrease the manufacturing yield.
In order to solve the above problem, another conventional optical disk has been developed wherein metallic clusters are dispersed in a hydrocarbon matrix in a recording layer. According to the optical disk of this type, the metallic clusters absorb beam energy upon radiation of a laser beam, and the hydrocarbon matrix emits a gas, thereby locally forming protuberances on the surface of the recording layer.
According to the optical disk described above, the structure of the recording layer is simplified to improve the utilization efficiency of the laser beam. However, it is difficult to properly control the relationship between the energy intensity of the laser beam and the amount of gas produced from the organic layer, thereby decreasing productivity of such optical disks. For example, when the energy intensity of the write beam is too high, the recording layer immediately bursts. Conversely, when the beam intensity is too low, the production of gas from the recording layer is insufficient to result in proper projection of the recording layer. An optimal (allowable) range of the beam intensity is thus narrowed, restricting the laser unit design. The amount of gas produced from the recording layer also depends on the ratio of the hydrocarbon matrix to the metallic clusters. Therefore, it is difficult to determine an optimal beam intensity. In order to perform proper information recording, a strict relationship between the ratio of the hydrocarbon matrix to the metallic cluster in the recording layer and the beam intensity must be established. When the manufacturing process control is restricted to obtain the necessary ratio, the yield of the disks may be limited, i.e., productivity may be lowered, resulting in high cost. The drawback of the conventional optical disk is due to insufficient thermal stability of the hydrocarbon matrix.